The Departed and Blood Diamond?

I am a huuuuuuuuuugggggggeeeeeee Leonardo DiCaprio. He's an incredible actor and I love all his movies. I've seen all the ones that were rated PG-13, but I REALLY want to see The Departed and Blood Diamond, but they're rated R. I've already asked about Blood Diamond several times, so now I've asking about The Departed. Is it okay for a 14 year old to watch. I go o public school so it can't be worst than what I'm used to. Why is it rated R, is it good? I want to see it sooo bad!